Error using sym>convertChar (line 1580) Character vectors and strings in the first argument can only specify a variable or number. To evaluate character vectors and strings re
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I had been needed to used Marquardt's Method for Multiple Variable Functions, but the code of I search on online has a bit problems. which the code given as below:
%Marquardt's Method for Multiple Variable Functions
clc;
close all;
%Insert starting points
x01=0;
x02=0;
%Function F in Symbolic Format
a='(x1^2+x2-11)^2+(x1+x2^2-7)^2';
%Insert the desired magnitude of final direction vector (0.0001 is fine)
eserror=0.0001;
Max_Iterations=20000;
convergance_criterion=0.0001;
k=0
gamma=100
%Leave the rest unchanged
%=================================
syms x1 x2
syms alpha real %difining alpha as real prevents matlab to solve function with conj(alpha)
% Hessian Of F
A=[diff(diff(a,x1),x1),diff(diff(a,x1),x2);...
diff(diff(a,x2),x1),diff(diff(a,x2),x2)]
%First Order Derivative of F
B=[diff(a,x1);diff(a,x2)];
% pretty(simplify(A))
subs(subs(A,x1,x01),x2,x02)
mag_of_B=sqrt(subs(subs(diff(a,x1),x1,x01),x2,x02)^2+subs(subs(diff(a,x2),x1,x01),x2,x02)^2)
records=[];
while (mag_of_B>convergance_criterion)&(k<Max_Iterations)
k=k+1;
temp=([x01;x02]-inv(subs(subs(A,x1,x01),x2,x02)+gamma*eye(size(subs(subs(A,x1,x01),x2,x02))))*(subs(subs(B,x1,x01),x2,x02)))'
disp('x1 x2');
[x01;x02]
disp('Hk')
subs(subs(A,x1,x01),x2,x02)
disp('gamm es');
gamma*eye(size(subs(subs(A,x1,x01),x2,x02)))
disp('diff');
(subs(subs(B,x1,x01),x2,x02))
disp('------------');
F_eval_old=subs(subs(a,x1,x01),x2,x02);
x01=temp(1,1);
x02=temp(1,2);
F_eval_new=subs(subs(a,x1,x01),x2,x02);
if F_eval_new<F_eval_old
gamma=.5*gamma;
else
gamma=2*gamma;
end
mag_of_B=sqrt(subs(subs(diff(a,x1),x1,x01),x2,x02)^2+subs(subs(diff(a,x2),x1,x01),x2,x02)^2)
records=[records;[k,x01,x02,subs(subs(a,x1,x01),x2,x02)]];
end
records
The error might be due to the version I used is 2021b, but i didn't know which part should i changed to clear the error. this is the error of the code:
Error using sym>convertChar (line 1580)
Character vectors and strings in the first argument can only specify a variable or number. To evaluate character vectors and
strings representing symbolic expressions, use 'str2sym'.
Error in sym>tomupad (line 1296)
S = convertChar(x);
Error in sym (line 234)
S.s = tomupad(x);
Error in sym/privResolveArgs (line 1016)
argout{k} = sym(arg);
Error in sym/diff (line 22)
args = privResolveArgs(S,varargin{:});
Error in ww (line 25)
A=[diff(diff(a,x1),x1),diff(diff(a,x1),x2);...
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采纳的回答
Shivang
2023-9-5
Hi Tan,
I understand you're running into an error regarding the use of symbolic expressions in your code.
Note that you cannot directly define symbolic expressions as a string or character vector. The following line in your code causes the above error:
a='(x1^2+x2-11)^2+(x1+x2^2-7)^2';
To evaluate a string representing a symbolic expression, use the 'str2sym' function. Replace the above line in your code with:
a= str2sym('(x1^2+x2-11)^2+(x1+x2^2-7)^2');
You should no longer see any symbolic expression related errors in your code.
Hope this helps.
-Shivang
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